1. Field of the Invention
The invention relates to a device for generating an electric field and more particularly to such devices of small physical dimension producing a comparatively high-strength electric field.
2. Prior Art
In certain applications, physically small electrical devices are needed to produce a relatively strong electric field. Once such application is in navigation gyroscopes, particularly in a small navigation gyroscope referred to as a Dry Tuned-Rotor Gyroscope (DTG). On particular type of DTG is described in the paper entitled Two-Axis Dry Tuned-Rotor Gyroscopes: Design and Technology; William M. Mansour and Corrado Lacchini, The American Institute of Aeronautics and Astronautics, Inc., Volume 16, No. 3, May-June 1993. The DTG is a two-degree-of-freedom sensor of angular velocity about two mutually orthogonal axes. This class of instruments has been adopted for a number of control applications, most notably in the navigation of ships, aircrafts, and other vehicles. The basic structure of one prior art DTG is shown in FIG. 1. The unit 100 shown in FIG. 1 comprises a housing assembly having a base 101 and a cover 102. The base 101 supports a spin shaft 104 on a pair of ball bearings 106. Mounted on the base 101 is a stator 107 forming part of a hysteresis motor. A hysteresis ring 108 is supported on the spin shaft. Flexibly supported on the shaft 104 is a rotor 110. A pair of permanent magnets 112, 114, which are vertically separated by means of a spacer 115, are mounted on rotor 110. The rotor 110 is flexibly mounted on the spin shaft 104 and is movable with respect to the spin shaft 104 about axes in a horizontal plane extending perpendicular to the plane of the cross section shown in FIG. 1. Torquer coils 120, 121 are mounted on a beryllium ring 122 supported on the base 101 and surrounding the magnets 112, 114. A pair of pick-offs 126 is mounted on the base 101. The pick-offs are well-known sensors coils producing an electrical output signal which varies with a variation in the spacing between the pick-offs and the rotor 110. It will be apparent from FIG. 1 that an angular displacement of the rotor 110 about an axis perpendicular to the plane of the cross section of FIG. 1 will result in an increase in the spacing between one of the two pick-offs 126 and the rotor 110 and a decrease in spacing between the other of the two pick-offs 126 and rotor 110. Electrical signals produced by the pick-offs are indicative of the magnitude of the angular displacement and are employed to produce a current in the torquer coils 120, 121. The torquer coils produce a magnetic field in the rotor 110 imparting a torque to the rotor 110 tending to return the rotor to a position such that the distances between the two pick-offs 126 and the rotor 110 are again equal.
The permanent magnets 112, 114 are ring magnets extending circumferentially within the rotor 110. The unit 100 comprises four separate pick-offs coils and four separate torquer coils. One set of pick-offs and one set of torquer coils are disposed along a horizontally extending x axis and equidistant from a vertical axis and are referred to as the x pick-offs and the x torquer coils, respectively. Similarly, a set of pick-offs, referred to as y pick-offs, and a set of torquer coils, referred to as y torquer coils, are disposed along a horizontally extending y axis, extending perpendicularly to the x axis, and spaced equidistant from the vertical axis. It will be apparent that only one of the sets of pick-offs and torquer coils is shown in FIG. 1. The other pick-offs and torquer coils are disposed at 90.degree. angles from those shown in FIG. 1. In operation, signals from the x and y pick-offs are 0 in the absence of angular displacement of the rotor 110 relative to the spin shaft 104. When such a displacement occurs about the y axis, the gap between one of the x pick-offs and the rotor will increase and the gap between the other of the x pick-offs and the rotor will decrease. To cancel the difference between the gaps, a torque is applied about the x axis to force the rotor to precess about the y axes. Accordingly, a signal derived from the x pick-offs is used to apply a current to the y torquer coils until the spacing between the rotor and the two x pick-offs is again equal.
Prior art torquer coils consist of several hundred turns of fine wire coated with an insulated coating. The coils of wire are formed or "blocked" into a special shape and bonded to maintain that shape. Two lead wires must be attached to each coil. Each of the four coils must then be affixed with an adhesive to the beryllium ring or the like in a precise location which varies from unit to unit due to the lack of precision inherent in the blocking operation. The eight lead wires are then soldered to a circuit board. It will be appreciated that the rate at which the rotor is returned to the level position, once it has experienced an angular displacement, is directly proportional to the magnetic force generated by the torquer coils. The force or moment applied by the torquer coil is a function of the number of turns of the torquer coil, the curved length of the coil (i.e., the length of the coil along the circumference of the beryllium ring), as well as the current in the coil. A disadvantage of the prior art arrangement is that the curved length of the coil is limited by the circumference of the beryllium ring which is preferably kept as small as reasonably possible since the diameter of the ring affects the total size of the device. Furthermore, the straight portion of the wound coil is necessarily relatively short since a significant portion of the overall dimension of the coil is consumed by the curved portion of the wound coil. Additionally, spacing between adjacent coils is necessary for electrical connections. Thus, even though each coil theoretically may occupy 90.degree. of the circumference of the ring, the straight portion of the coil, which determines curved length, may occupy only about 60.degree.. To be useful in high-speed missiles and the like, the gyro must be of small size and must correct at a very high rate in order to be able to detect attitude changes of the vehicle at a sufficiently fast rate. To obtain a high rate of correction, a rapidly varying, high-strength magnetic field is required. However, the amount of current that can be supplied to the small size coil is limited due to excessive heat which is generated in the wire.